1. Field of the Invention
This invention pertains to a powertrain for use in a motor vehicle driven from a prime mover that has a high idle speed and a high maximum speed. More particularly, this invention pertains to the powertrain for such a motor vehicle that provides two paths for torque transmission through the torque converter to the various gearsets of the transmission.
2. Description of the Prior Art
Certain electrical motors that can be applied to drive a motor vehicle are d.c. motors having field weakening techniques to control the motor operation. Such motors are characterized by a base or idle speed that approximates one-half of the maximum speed of the motor. Consequently, transmissions operating in conjunction with these motors require some means for accommodating the high idle speed when the vehicle is driven from a standing start. The transmission must also be able to produce reverse drive with the motor turning in one direction only.
The operating range of a vehicle powered by an electrical motor is crucial to its commercial acceptance and success. Power losses particularly those associated with operation of the torque converter must be held as low as possible yet a hydrokinetic torque converter is required for start-up operation. The vehicle range can be extended if the transmission can accommodate regenerative braking, wherein the kinetic energy of the vehicle is recovered and converted to electrical energy to charge the batteries, the process acting to brake the vehicle.
The hydraulic control system that operates to actuate the clutches and brake bands of the transmission is a source of inefficiency that reduces the range of the vehicle. The transmission for an electrical vehicle should minimize the losses and preferably allow the vehicle to be operated in at leat one forward speed ratio with the hydraulic control system inoperative.
The vehicle in which an electric drive will be used will provide minimal space for the motor and transmission. Accordingly, the powertrain should be transversely mounted parallel to the wheel axles and preferably concentric with the axis of the drive wheels. The transmission should provide hill braking in at least one forward speed ratio wherein the motor can be used to brake the vehicle in cooperation with or independent of the wheel brakes. The kinetic energy can be recovered and used to charge the batteries when the vehicle is coasting.